Question: 2 rubber stamps cost $3.68. Which equation would help determine the cost of 13 rubber stamps?
There are several equations that could help determine the cost, each with a slightly different approach. We can write the fact that 2 rubber stamps cost $3.68 as a proportion: $\dfrac{2}{\$3.68}$ Let $x$ represent the unknown cost of 13 rubber stamps. Since 13 rubber stamps cost $x$ , we have the following proportion: $\dfrac{13}{x}$ The cost changes along with the number of rubber stamps purchased, and so the two proportions are equivalent. $\dfrac{2}{\$3.68} = \dfrac{13}{x}$